How South America Went From a Haven of Stability to a Mess in 18 Months

SANTIAGO, Chile—Imagine an Obama administration official looking out at the world from the vantage point of December 2015. The Middle East is engulfed in bloody conflict and crackdowns on domestic dissent. Africa is muddling through a humbling correction to the “success story” narrative that had been used to portray the continent’s preceding decade of dynamic growth and democratic progress. Asia is an uneasy landscape of shifting power balances and wary hedging in the shadow of a newly aggressive China. And Europe is struggling to address a refugee and migrant crisis that is awakening a populist backlash to elite consensus.

At the time, if there was one part of the world that the administration could have felt reasonably certain it would pass off to its successor in better shape than when Barack Obama took office in 2008, it was Latin America, and in particular South America. ...